Despite well-documented deficits in speech naturalness, there are few techniques available to enhance speech naturalness in individuals with Parkinson's disease (PD). Thus, there is a critical need to identify and quantify the effectiveness of therapy techniques that enhance speech naturalness in individuals with PD, thereby improving overall communicative effectiveness. The overall objective of this proposal is to assess the positive benefits of a respiratory treatment, Expiratory Muscle Strength Training (EMST), for improving speech naturalness in individuals with PD. The deficits in speech naturalness associated with PD targeted in this proposal include impairments in stress patterns, utterance length, and pausing behaviors. Individuals with PD are less able to produce active muscle forces to respond to the variety of demands placed on the respiratory system during speech. Because decreased speech naturalness is at least partially due to decreased expiratory muscle strength, the EMST paradigm is designed to directly enhance expiratory muscle strength. As a result of increased expiratory muscle strength post-EMST, individuals with PD will utilize increased active muscle forces to better respond to the demands of speech. Changes to communicative effectiveness, specifically speech naturalness, as a result of EMST have yet to be investigated. The rationale for the proposal is that successful completion will lead to the firs evidence-based treatment technique specifically designed to target speech naturalness in individuals with PD. The three specific aims of the proposal are: 1) to assess the effectiveness of EMST for improving global measures of communicative effectiveness in individuals with PD, 2) to identify the underlying physiologic changes to respiratory support for speech as a result of EMST, and 3) to identify the underlying speech characteristics that are altered in response to EMST and that contribute to changes in speech naturalness. To address these aims, a pre-test-post-test design with multiple baseline measures and a 4-week training period will be used. Perceptual ratings of intelligibility and speech naturalness, respiratory kinematics, and acoustic analyses of intonation, stress, and pause patterns will be used to determine the efficacy of the treatment. This contribution is significant because it is the first step in a continuum of research that is expected to lead to the development of respiratory interventions designed to improve communicative effectiveness in individuals with PD. Successful completion of this project will provide clinicians with an evidence-based treatment technique for reduced speech naturalness in individuals with PD that improves both functional speech outcomes and physiology. PUBLIC HEALTH RELEVANCE: The proposed research is relevant to public health because it is expected to provide an evidence-based treatment technique to enhance speech naturalness in individuals with PD. The treatment is innovative because it focuses on direct improvement of respiratory support for speech as a way to enhance speech naturalness without relying on an individual's cognitive abilities.